Hailey, Idaho (CNN) -- The father of the only American POW in Afghanistan sent a message to his son's Taliban captors on Saturday: "After 12 years, let there be peace. Can we push this forward and make it happen?"
And he sent a message to his son: "I will not leave you on the battlefield. You are not forgotten."
Updates about Sgt. Bowe Bergdahl's case have been sparse since he was captured nearly four years ago after finishing a guard shift at a combat outpost.
Family members have remained reticent for fear of jeopardizing his safety.
But the 27-year-old soldier's parents spoke out at a rally in home state of Idaho on Saturday, just days after U.S. authorities said discussion of a possible prisoner exchange with the Taliban could be on the table during upcoming talks.
"We are feeling optimistic this week," mother Jani Bergdahl said. "So many of you have come from far away, and we appreciate the sacrifices you made to make this possible."
More than 1,000 people were in the crowd, including hundreds of war veterans who rode motorcycles into this town.
Throughout the event, they chanted, "Bring Bowe Home."
Local politicians, state senators and police officials also spoke at the event.
"We hope he will see this and know of you," his mother told the crowd. Then, she sent a message to her son, "We love you and are eagerly awaiting your return home."
In a statement released earlier this week through a family spokesman, the soldier's parents said they were encouraged by word that upcoming negotiations might lead to their son's freedom.
"That is encouraging news, especially after not much encouraging news over the past four years," Army Col. Tim Marsano said, adding that the Bergdahls have been talking with military and government agencies. "They know their son has not been forgotten. My brothers and sisters in uniform know we won't rest until Bowe Bergdahl is safely back with his family."
At Saturday's rally, father Bob Bergdahl sported a long beard, which he has grown out since his son's capture as a sign of solidarity. And he spoke briefly in Pashto, a language that he's studied during his son's captivity. He offered a message that he said was meant for the Taliban.
"May the peace of God and blessings of God be upon you," he said. "After 12 years, let there be peace. Can we push this forward and make this happen?"
Speaking in English, he offered a message in English that he said was meant for his son.
"Bowe, my son, if you can hear me. ... you are part of the peace process, you are part of ending the Afghan war. Have faith. Do good works. Tell the truth, and have the patience that can only come from God. We are being tested," Bob Bergdahl said.
On Thursday, State Department spokeswoman Jennifer Psaki said the U.S. expects prisoner exchange to be a topic of talks with the Taliban, which are slated to take place "in the coming days," in Doha, Qatar.
No decisions have been made about transferring any Taliban detainees held at Guantanamo Bay. Any such decision would have to be made with congressional approval and in accordance with U.S. law, she said.
It won't be the first time U.S. negotiators raise the issue of Bergdahl's release with the Taliban. The two sides held meetings in 2011 and 2012 that included the topic of Bergdahl's release, with sporadic discussions since then.
While the United States has been pushing for the return of Bergdahl -- captured in June 2009 in Afghanistan -- the Taliban has been pushing for the release of five of its own men from U.S. custody in Guantanamo Bay. Psaki said the United States expects the Taliban will raise that issue again when the two sides meet.
In the meantime, Bergdahl's father said Saturday that he'll never stop pushing for his son's freedom.
"A father does not leave his son on the battlefield. I live in Afghanistan, my phone on Afghan time," he said. "I will not leave you on the battlefield. You are not forgotten. You will not be forgotten. We pray soon you will come home."
CNN's Eliott C. McLaughlin and Melissa Gray contributed to this report.